1. Field of the Invention
This invention relates to a photosensitive lithographic printing plate precursor having an ultra-high photographic speed, an excellent ink receptivity, a good tonal reproduction and a high printing durability and a method of producing a printing plate therefrom, and in particular to a pre-sensitized plate (referred to hereinafter as a PS plate) based on the photosensitivity of silver halide and a method for preparing a printing plate therefrom.
2. Description of the Prior Art
Various types of PS plates utilizing the photosensitivity of silver halide have been described in the art, for example, in Japanese Patent Publication Nos. 27242/69, 16725/73, and 30562/73, British Pat. No. 1,567,844, U.S. Pat. Nos. 4,173,477, 3,083,097, 3,161,508, 3,721,559 and 3,146,104, etc. Such plates, however, exhibit defects such as low printing durability, a tendency to generate stain, or poor oleophilicity at image areas. In order to eliminate such deficiencies, other types of high-speed PS plates have been proposed in which a silver halide photographic emulsion coating is provided on the surface of a conventional PS plate having a non-silver photosensitive layer. Such plates are disclosed, for example, in Japanese Patent Publication No. 26521/71, Japanese Patent Application (OPI) No. 27804/79 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application"), German Patent Application (OLS) Nos. 2,517,711, 2,640,763, etc. Other improved types of plates are described in, for example, U.S. Pat. No. 3,245,793, U.S. Defensive Publication No. T870,022, Japanese Patent Publication No. 23721/72, etc., in which an intermediate layer is present between the non-silver photosensitive layer and the silver halide containing photographic coating. Provision of such an intermediate layer, however, raises the manufacturing cost, and further suffers from a poor printing durability and oleophilicity in comparison to the one without such an intermediate layer. Moreover, when the thickness of the intermediate layer exceeds about one micron, the reproducibility of the image forming behavior deteriorates. To overcome this defect, still other types of PS plates have been disclosed in Japanese Patent Application (OPI) Nos. 74258/79, 76162/79 and 100596/79. Unfortunately, these types of plates still exhibit many drawbacks; as TAGA Proceedings pointed out (1975, pp. 1-22), when such a high-speed PS plate can be used for projection plate making, the fidelity of the reproduced image drastically deteriorates with the increase of magnification ratio when the original contains a very fine image or halftone images with a high dot density. The increase of the magnification ratio also causes the tonal range of a screened image to shrink.